Added is_distinct_from() method

Author: erezsh

data_diff/databases/base.py

@@ -270,9 +270,13 @@ def offset_limit(self, offset: Optional[int] = None, limit: Optional[int] = None
         return f"LIMIT {limit}"
 
     def concat(self, l: List[str]) -> str:
+        assert len(l) > 1
         joined_exprs = ", ".join(l)
         return f"concat({joined_exprs})"
 
+    def is_distinct_from(self, a: str, b: str) -> str:
+        return f"{a} is distinct from {b}"
+
     def timestamp_value(self, t: DbTime) -> str:
         return f"'{t.isoformat()}'"
 

data_diff/databases/database_types.py

@@ -149,6 +149,11 @@ def concat(self, l: List[str]) -> str:
         "Provide SQL for concatenating a bunch of column into a string"
         ...
 
+    @abstractmethod
+    def is_distinct_from(self, a: str, b: str) -> str:
+        "Provide SQL for a comparison where NULL = NULL is true"
+        ...
+
     @abstractmethod
     def timestamp_value(self, t: DbTime) -> str:
         "Provide SQL for the given timestamp value"

data_diff/databases/mysql.py

@@ -69,3 +69,6 @@ def normalize_number(self, value: str, coltype: FractionalType) -> str:
 
     def normalize_uuid(self, value: str, coltype: ColType_UUID) -> str:
         return f"TRIM(CAST({value} AS char))"
+
+    def is_distinct_from(self, a: str, b: str) -> str:
+        return f"not ({a} <=> {b})"